1. Field of the Invention
The invention concerns apparatus for determining the effects of dilution and/or diffusion on the gaseous components of a gas flow passing through a gas-permeable test-object, with a suction source drawing a calibrating gas at least through part of the test-object, a volumeter for the calibrating gas flowing into the test-object and a concentration testing means for the gas issuing from the test-object. Such apparatus is suited for testing arbitrary gas-permeable test-objects, for instance filter plugs, filter rods, cigars and cigarettes.
2. Description of the Prior Art
While many publications have examined the changes in concentration of the mainstream smoke of cigarettes during combustion, the effects of dilution and diffusion on the concentration of gaseous components on account of the experimental difficulties involved have been researched only recently. This is because the effects of diffusion and dilution could not be empirically distinguished from the combustion-induced generation of gases.
However, as the gaseous components of the smoke, in particular the so-called low-molecular weight gases such as nitrogen, hydrogen, methane, carbon monoxide, carbon dioxide and nitric oxides have become significant, apparatus was developed to determine the effects of dilution and diffusion on the gaseous components of the cited species in the flow of smoke (BEITRAEGE ZUR TABAKFORSCHUNG, vol. 9, issue 3, October 1977, pp 141).
In that procedure, a calibrating gas is drawn out of a gas pouch and through a cigarette by a smoking machine and then is analyzed quantitatively, that is, the concentration of the gas in the flow issuing from the cigarette is determined. Prior to each test series, the calibrating gas is made to pass through a soap-bubble buret to determine the volume of the calibrating gas flowing into the cigarette. Given the constant stroke of the smoking machine and hence the constant volume aspirated by the smoking machine, the volume of the calibrating gas flowing into the cigarette and the measured concentration of the issuing gas, the change in concentration of the calibrating gas can be ascertained, which is due to the diffusion of the calibrating gas through the cigarette paper outward and also to the ambient gas rarefying the calibrating gas which is aspirated through the cigarette paper into the cigarette. The calibrating gas is made to pass from a compressed gas contained into the gas pouch because the calibrating gas' pressure may not exceed that of the atmosphere around the cigarette.
In practice, especially in routine monitoring tests on cigarettes, there were several drawbacks in this prior art apparatus. First, operating a soap-bubble buret is extremely complex, time-consuming and susceptible to errors. Second, the concentration of a calibrating gas passed from the gas bottle into the gas pouch and the gas pouch on account of inadequate seals, had an influx of foreign gas during handling, and residual gases due to incomplete evacuation of the gas pouch. The system was thus susceptible to variations which could not be checked unless there was access into the otherwise closed measuring system.
Lastly, the flow rate of the gas entering the cigarette can not be measured during the testing properly because the calibrating gas passed through the soap-bubble buret can't be used for measuring the dilution and diffusion in view of the water vapor that was absorbed.